A wide variety of medication delivery pumps are known. In general, these pumps are configured to deliver a fluid from a source to a patient under pressure.
In order for the pump to be re-usable, at least the portion of the pump which contacts the fluid must be sterilizable. This is difficult for integral pumps where the pumping mechanism and fluid path are part of a single unit. For this reason, pumps have been developed with have a re-usable pumping unit which cooperates with a fluid path element. In this manner, the fluid path element can be separated from the pumping unit for sterilization and reuse.
These reusable pumps, however, suffer from a number of drawbacks. First, many designs are highly complex, resulting in high costs of manufacture and maintenance costs, and low reliability. In addition, the pumps generally suffer from one or more design issues which result in less than optimum performance. For example, it is desirable for the pump to include a flow sensor, and yet such a feature is often inconsistent with the design of the re-usable pump. Also, these pumps generally have undesirable compliance. “Compliance” is a measure of the volume per unit pressure change in region between intake and outlet of the pump. Many commercial pumps suffer significantly due to undesirable compliance resulting in either significant change to average and instantaneous flow when varying intake and output pressures are experienced.
For example, one re-usable pump design is represented by the IVAC 500 series (550, 570, 580, etc.) linear peristaltic pumps. These pumps use sequentially occluding fingers to peristaltically advance fluid by advancing an occlusion point from the intake end to the outlet end of a second of tubing. Compliance of the tubing governs the sensitivity of average flow to intake pressure. The average flow of these pumps is quite insensitive to output pressure. However, flow uniformity is degraded with increasing output pressure and pump segment compliance.
Other examples of re-usable pumps are the Alaris LVP Module and Asena GP pumps. These are dual chamber pumps using conventional cylindrical tubing together with two active pumping regions and two valves, one above the upper region and the second between the upper and lower pumping region. The net filling volume of the upper pump region defines the cyclic volume pumped and due to the elasticity of this region, variation of intake pressure affects the actual volume delivery. The lower pump region delivers fluid while the upper chamber is filling, resulting in smoothing of flow output. If elevated output pressure exists, when the lower occlude opens, fluid moves retrograde into the upper pump region. When the upper occluder opens, this excess volume moves back into the drip chamber, thus reducing net volume pumped and disturbing uniformity of flow. A second drawback of dual chamber pumps is the likelihood of air being entrained within the pumping chambers. When this occurs, not only is the compliance increased, but the net pumping volume is directly diminished.